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Spiders are nature's engineers that build lightweight and high-performance web architectures often several times their size and with very few supports; however, little is known about web mechanics and geometries throughout construction, especially for three-dimensional (3D) spider webs. In this work, we investigate the structure and mechanics for a Tidarren sisyphoides spider web at varying stages of construction. This is accomplished by imaging, modeling, and simulations throughout the web-building process to capture changes in the natural web geometry and the mechanical properties. We show that the foundation of the web geometry, strength, and functionality is created during the first 2 d of construction, after which the spider reinforces the existing network with limited expansion of the structure within the frame. A better understanding of the biological and mechanical performance of the 3D spider web under construction could inspire sustainable robust and resilient fiber networks, complex materials, structures, scaffolding, and self-assembly strategies for hierarchical structures and inspire additive manufacturing methods such as 3D printing as well as inspire artistic and architectural and engineering applications., Competing Interests: The authors declare no competing interest.

In light of recent focus on the behaviour of the natural structures for revolutionary technological growth, spider web seems to have seized considerable attention of product designer due to its amazing behaviour. In present work, mechanism behind the structural integrity of the spider web along with the materialistic analysis of its constituent silk threads has been extensively investigated. The nanoindentation tool both in static and dynamic mode has been utilized for complete analysis of the mechanical behaviour of the spiral and radial threads separately. Both the average elastic modulus and hardness of the radial silk thread is higher than the spiral silk thread which reveals the radial silk thread is the major structural component of the web. The sustainability of spider webs under storm, windy conditions and during the impact of pray has been investigated under dynamic conditions. The radial silk thread exhibits elastic like response and the spiral silk thread exhibits viscous like response in a wide frequency range (1-200Hz). The damping characteristic of the radial and spiral silk threads, an important parameter to investigate the energy dissipation properties of the materials has also been investigated in windy conditions., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

Millions of years of evolution have adapted spider webs to achieve a range of properties, including the well-known capture of prey, with efficient use of materials. One feature that remains poorly understood is the attachment disc, a network of silk fibers that mechanically anchors a web to its environment. Experimental observations suggest that one possible attachment disc adheres to a substrate through multiple symmetrically branched structures composed of sub-micrometer scale silk fibers. Here, a theoretical model is used to explore the adaptation of the strength of attachment of such an anchorage, and complementary mesoscale simulations are applied to demonstrate a novel mechanism of synergetic material and structural optimization, such that the maximum anchorage strength can be achieved regardless of the initial anchor placement or material type. The optimal delamination (peeling) angle is facilitated by the inherent extensibility of silk, and is attained automatically during the process of delamination. This concept of self-optimizing peeling angle suggests that attachment discs do not require precise placement by the spider, irrespective of adhesion strength. Additional hierarchical branching of the anchorage increases efficiency, where both the delamination force and toughness modulus increase with a splitting of the cross-sectional area., (Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Recent, rapid arthropod declines have been tied to human activity. Yet, the propensity for human‐produced noise to disturb the substrate‐borne (vibratory) channel remains virtually untested despite arthropods' ubiquitous use of vibratory information. Characterizing the vibratory landscape at biologically relevant scales is an essential initial step. We aimed to measure vibratory noise across space and time to assess its potential overlap with the urban–rural range and season of a funnel‐weaving spider, Agelenopsis pennsylvanica (C.L. Koch) (Araneae: Agelenidae), a common urban arthropod. We assessed 24‐h ambient vibrations (hereafter vibratory "noise") at 23 sites across urban–rural Lincoln, Nebraska (NE, USA), during the adult season of A. pennsylvanica (August–October). Vibratory noise (amplitude, Leq) varied by ~15 dB across sites overlapping with frequencies within A. pennsylvanica's sensitivity (20–1000 Hz). Urban vibratory noise was positively correlated with the principal component containing estimates of traffic‐induced vibrations (e.g., traffic volume, road proximity, and impervious cover), whereas rural noise levels correlated with probable harvest times. Our findings indicate spatial variation in noise in urban areas and seasonal noise variability in rural areas. We also tested how A. pennsylvanica—collected from four distinct noise survey sites—use their vibratory microhabitat. We assessed daily spider position and dry silk mass within a microcosm that played loud and quiet vibrations (white noise differing by ~15 dB) in separate but connected chambers. Age affected the chamber choice (hereafter "microhabitat use") of spiders collected from the loudest site, as younger adults associated with and used more silk in the loud chamber, but this effect decreased with age. As our data demonstrate that vibratory noise varies with A. pennsylvanica's microhabitat and season with a high potential for impacting behavior, we hypothesize that this environmental noise likely impacts other arthropods as well. [ABSTRACT FROM AUTHOR]

Spider silk is a promising material with great potential in biomedical applications due to its incredible mechanical properties and resistance to degradation of commercially available bacterial strains. However, little is known about the bacterial communities that may inhabit spider webs and how these microorganisms interact with spider silk. In this study, we exposed two exopolysaccharide-secreting bacteria, isolated from webs of an orb spider, to major ampullate (MA) silk from host spiders. The naturally occurring lipid and glycoprotein surface layers of MA silk were experimentally removed to further probe the interaction between bacteria and silk. Extensibility of major ampullate silk produced by Triconephila clavata that was exposed to either Microbacterium sp. or Novosphigobium sp. was significantly higher than that of silk that was not exposed to bacteria (differed by 58.7%). This strain-enhancing effect was not observed when the lipid and glycoprotein surface layers of MA silks were removed. The presence of exopolysaccharides was detected through NMR from MA silks exposed to these two bacteria but not from those without exposure. Here we report for the first time that exopolysaccharide-secreting bacteria inhabiting spider webs can enhance extensibility of host MA silks and silk surface layers play a vital role in mediating such effects. [ABSTRACT FROM AUTHOR]

The web-building skills of spiders made them strong from the evolutionary aspect. Spider webs are used in hunting, building nests, setting traps, and movement. The structure of web architecture, that of adhesive materials being produced, and that of cribellate offer important clues in order to understand their hunting behaviors. Spiders have different silk-spinning apparatuses, allowing them to produce different types of silk fibrils. While some spider species rely on webs for survival in nature, others can survive without them. Even though basic taxonomic features remain constant, the silk-spinning apparatuses of spiders might be subjected to adaptive variations. In the present study, the structural organization of the silk-spinning apparatus and the web architecture of the web-maker spider Uloborus walckenaerius Latreille, 1806 were observed by making use of scanning electron microscopy (SEM). The web structure of U. walckenaerius, the characteristics of the spinnerets, especially the posterior spinneret, and the arrangement of the spigots are reported in this study. Adaptations of the silk-spinning apparatus, which has provided an evolutionary success to U. walckenaerius, were also analyzed. It was determined that the web structure consisted of very fine nanofibers and, differing from other groups, there also were crimped silk fibrils. [ABSTRACT FROM AUTHOR]

The development of bio‐inks capable of being 3D‐printed into cell‐containing bio‐fabricates with sufficient shape fidelity is highly demanding. Structural integrity and favorable mechanical properties can be achieved by applying high polymer concentrations in hydrogels. Unfortunately, this often comes at the expense of cell performance since cells may become entrapped in the dense matrix. This drawback can be addressed by incorporating fibers as reinforcing fillers that strengthen the overall bio‐ink structure and provide a second hierarchical micro‐structure to which cells can adhere and align, resulting in enhanced cell activity. In this work, the potential impact of collagen‐coated short polycaprolactone‐fibers on cells after being printed in a hydrogel is systematically studied. The matrix is composed of eADF4(C16), a recombinant spider silk protein that is cytocompatible but non‐adhesive for cells. Consequently, the impact of fibers could be exclusively examined, excluding secondary effects induced by the matrix. Applying this model system, a significant impact of such fillers on rheology and cell behavior is observed. Strikingly, it could be shown that fibers reduce cell viability upon printing but subsequently promote cell performance in the printed construct, emphasizing the need to distinguish between in‐print and post‐print impact of fillers in bio‐inks. [ABSTRACT FROM AUTHOR]

Silk has a long history as an exclusive textile, but also as a suture thread in medicine; nowadays, diverse cell carriers are manufactured from silk. Its advantages are manifold, including high biocompatibility, biomechanical strength and processability (approved for nearly all manufacturing techniques). Silk's limitations, such as scarcity and batch to batch variations, are overcome by gene technology, which allows for the upscaled production of recombinant "designed" silk proteins. For processing thin fibroin filaments, the sericin component is generally removed (degumming). In contrast to many synthetic biomaterials, fibroin allows for superior cell adherence and growth. In addition, silk grafts demonstrate superior mechanical performance and long-term stability, making them attractive for anterior cruciate ligament (ACL) tissue engineering. Looking at these promising properties, this review focusses on the responses of cell types to silk variants, as well as their biomechanical properties, which are relevant for ACL tissue engineering. Meanwhile, sericin has also attracted increasing interest and has been proposed as a bioactive biomaterial with antimicrobial properties. But so far, fibroin was exclusively used for experimental ACL tissue engineering approaches, and fibroin from spider silk also seems not to have been applied. To improve the bone integration of ACL grafts, silk scaffolds with osteogenic functionalization, silk-based tunnel fillers and interference screws have been developed. Nevertheless, signaling pathways stimulated by silk components remain barely elucidated, but need to be considered during the development of optimized silk cell carriers for ACL tissue engineering. [ABSTRACT FROM AUTHOR]

Dragline silk fibers produced by spiders are a masterpiece structural protein that is durable even in the wild conditions. Dragline silk fibers are known to have excellent mechanical toughness and flexibility and further possess optical transparency, which are highly promising as textiles, sensors, and optical devices. Here, the authors show that the dragline silk microfibers act as good optical waveguides with the optical loss coefficient as small as 0.03 decibel per micrometer. The light transportation in the dragline silk fiber is performed by fluorescence energy transfer between two microspheres located on a suspended dragline silk microfiber. By utilizing a micromanipulation equipment, micrometer‐scale spider web‐like structures are fabricated. The experimentally observed optical waveguiding properties of the weaves match well with simulation results using simple mathematical models. Furthermore, optical logic gate operations are demonstrated using photoswitchable microsphere resonators attached on the dragline fibers. [ABSTRACT FROM AUTHOR]

Much genomic-scale, especially transcriptomic, data on spider phylogeny has accumulated in the last few years. These data have recently been used to investigate the diverse architectures and the origin of spider webs, concluding that the ancestral spider spun no foraging web, that spider webs evolved de novo 10-14 times, and that the orb web evolved at least three times. These findings in fact result from a particular phylogenetic character coding strategy, specifically coding the absence of webs as logically equivalent, and homologous to, 10 other observable (i.e., not absent) web architectures. "Absence" of webs should be regarded as inapplicable data. To be analyzed properly by character optimization algorithms, it should be coded as "?" because these codes-or their equivalent-are handled differently by such algorithms. Additional problems include critical misspellings of taxon names from one analysis to the next (misspellings cause some optimization algorithms to drop terminals, which affects taxon sampling and results), and mistakes in spider natural history. In sum, the method causes character optimization algorithms to produce counter-intuitive results, and does not distinguish absence from secondary loss. Proper treatment of missing entries and corrected data instead imply that foraging webs are primitive for spiders and that webs have been lost ∼5-7 times, not gained 10-14 times. The orb web, specifically, may be homologous (originated only once) although lost 2-6 times.

Geometric regularity of spider webs has been intensively studied in orb‐weaving spiders, although it is not exclusive of orb weavers. Here, we document the geometrically regular, repetitive elements in the webs of the non‐orb‐weaving groups Leptonetidae and Telemidae for the first time. Similar to orb weavers, we found areas with regularly spaced parallel lines in the webs of Calileptoneta helferi, Sulcia sp., and cf. Pinelema sp. Furthermore, we provide a detailed account of the regular webs of Ochyrocera (Ochyroceratidae). The sections of the web with regularly disposed parallel lines are built as U‐shaped modules reminiscent of orb webs. It has been suggested that the regularly spaced parallel lines in the webs of Ochyroceratidae and Psilodercidae may be produced in a single sweep of their posterior lateral spinnerets, which have regularly spaced aciniform gland spigots, perhaps involving expansion of the spinnerets. To test this hypothesis, we compared the spacing between parallel lines with the spacing between spigots, searched for expansible membranes in the spinnerets, and examined the junctions of regularly spaced lines. The distance between parallel lines was 10–20 times the distance between spigots, and we found no expansible membranes, and the intersection of parallel lines are cemented, which opposes the single sweep hypothesis. Furthermore, we found cues of viscid silk in the parallel lines of the psilodercid Althepus and broadened piriform gland spigots that may be responsible of its production. Finally, we evaluated the presence or absence of geometrically regular web elements across the spider tree of life. We found reports of regular webs in 31 spider families, including 20 families that are not orb weavers and hypothesize that the two basic aspects of regularity (parallel lines spaced at regular intervals, and radial lines spaced at regular angles) probably appeared many times in the evolution of spiders. [ABSTRACT FROM AUTHOR]

The water-soluble glue substance of the capture threads in Trichonephila clavata is solely produced from two pairs of aggregate silk glands. During the web glue production, secretory vesicles were synthesized via the extensive rough endoplasmic reticulum of epithelial cells. Unlike the clearly described fibrous web production in spiders, the process of aqueous web glue production appears to involve either a condensing or a packaging step by the Golgi complex. In particular, the fine structure of secretory vesicles varies from cell to cell and may represent the secretory cycle. The electron-dense multivesicular bodies were clearly visible as discrete droplets, and the mature secretory product in the glandular epithelium appeared as a spherical vacuole grown by fusion with surrounding small vesicles. Our fine structural observation reveals that the secretion occurs when the release of secreted material involves the loss of part of the cytoplasm. The bleb along the luminal surface of the secretory cells and membrane-bound extracellular vesicles which pinched off from the cell suggests that the secretory product is released by the mechanism of apocrine secretion. [ABSTRACT FROM AUTHOR]

Orb-web weaving spiders use a variety of silk types for particular tasks, and each silk type is composed of at least two spider silk proteins (spidroins). In the early stage of divergence, however, the molecular evolutionary processes act on spidroin variants are still unclear because of a lack of knowledge for full-length paralogous and orthologous gene sequences among closely related species. Here, we present two complete gene sequences encoding the tubuliform spidroin TuSp1 variants (TuSp1-v2 and TuSp1-v3) from orb-weaving spider Neoscona theisi. Both N. theisi TuSp1-v2 and TuSp1-v3 genes contain a single enormous exon (14,139 bp for TuSp1-v2 and 13,152 bp for TuSp1-v3) and dozens of tandemly arrayed repeats (25 repeats for TuSp1-v2 and 23 repeats for TuSp1-v3) with extreme intragenic homogenization. The pattern of expression for these two spidroins revealed that the level of TuSp1-v3 mRNA is ~3-fold higher than that of TuSp1-v2 in tubuliform gland. Phylogenetic analyses of spidroins not only show the occurrence of a gene duplication event for TuSp1-v2 and TuSp1-v3 in the common ancestor of the Neoscona and Araneus lineage but reinforce the role of concerted evolution for the extreme homogenization of TuSp1 repeats. [ABSTRACT FROM AUTHOR]

Spiders often generate several forms of silk fiber, each with distinctive qualities befitting them with certain activities and biological processes. The egg sacs of spiders are multilayered, complex structures that contain fibers from a variety of glands. The female lays her eggs in egg sacs that are safe from both living and nonliving elements. There are a few reviews of spider webs and silk, but none of her egg sacs. Our understanding of the relationship between protein structure, mechanical characteristics, antimicrobial activity, and ecological role of these exceptional biomaterials will expand and improve by examining egg sac silk. We address the current state of knowledge about spider egg sac silk and its processing method, as well as the use of egg sac silk-based materials in biomedicine and materials engineering. This review elucidates the structure, fiber composition, defense mechanism, mechanical strength, coloration, and antimicrobial activity of egg sac silk fibers. Spider egg sac silk-based materials have the potential to lead to advanced resistant and usable materials, making them one of the most exciting areas of research in material science. Future researchers will be able to take a more holistic approach as a result of it. [ABSTRACT FROM AUTHOR]

Spider webs are iconic examples of extended phenotypes that are remarkably plastic across different environments. Orb webs are not only effective traps for capturing prey, but can also provide information to potential mates and, in some cases, potential predators and prey through silk-based chemicals. As with regular phenotypic traits, variability in the properties of spider webs is thought to be mediated by a combination of genetic and environmental effects. Here, we examined variation in several key features of the webs of the orb-weaving spider Argiope keyserlingi across five geographically disparate populations. We documented variation in web architecture and chemical properties of webs collected directly from the field. We then probed the potential for the underlying environmental driver of local insect abundance to explain this variation, by analysing the properties of orb webs constructed by the spiders from these different populations, but under identical laboratory conditions. We found no evidence of variation across populations in the architecture of webs constructed in the laboratory, despite the large geographic distances. Nonetheless, we discovered between population variation in the composition of chemicals found on the surface of silk and in the taxonomic distribution of available prey. Furthermore, there was a positive correlation between the quantity of nitrogenous compounds in web silks and female body condition. When combined, these findings suggest that environmental mechanisms can drive variation in web traits across spider populations. [ABSTRACT FROM AUTHOR]

Although camouflage as an effective antipredator defense strategy is widespread across animals, highly conspicuous color patterning is not uncommon either. Many orb‐web spiders adorn their webs with extra bright white silk. These conspicuous decorations are hypothesized to deter predators by warning the presence of sticky webs, camouflaging spiders, acting as a decoy, or intimidating predators by their apparent size. The decorations may also deflect predator attacks from spiders. However, empirical evidence for this deflection function remains limited. Here, we tested this hypothesis using the X‐shaped silk cruciform decorations built by females of Argiope minuta. We employed visual modeling to quantify the conspicuousness of spiders and decorations from a perspective of avian predators. Then, we determined actual predation risk on spiders using naïve chicks as predators. Spider bodies and decorations were conspicuous against natural backgrounds to the avian visual systems. Chicks attacked the spider main bodies significantly less frequently on the decorated webs than on the undecorated webs, thus reducing predation risk. When both spiders and decorations were present, chicks also attacked the spider main bodies and their legs or decorations, and not randomly: they attacked the legs or decorations sooner and more frequently than they attacked the main bodies, independent of the ratio of the surface area between the decoration and spider size. Despite the increase in detectability, incorporating a conspicuous cruciform decoration to the web effectively defends the spider by diverting the attack toward the decoration or leg, but not by camouflaging or intimidating, thus, supporting the deflection hypothesis. [ABSTRACT FROM AUTHOR]

Major ampullate silk is noted for its great tensile strength and extensibility. The impressive material properties of major ampullate silk result from their component proteins that encoded by members of the spidroin (spider fibroin) gene family. Although the major ampullate spidroin type has evolved multiple variants within specific-species, most sequences are fragmented. Here, we present two complete major ampullate spidroin genes from the orb-weaving spider Araneus ventricosus. Due to the abundant GPG motifs in their repetitive region, the two MaSp genes were grouped in MaSp2 subclass and named MaSp2C and MaSp2D, respectively. Analysis of the full-length gene sequences reveals that both of them include a single enormous exon (10,851 bp for MaSp2C and 8640 bp for MaSp2D) that mainly translates into a central repetitive region containing multiple amino acid motifs that can be organized into five ensemble types. We use gene-specific PCR primers to search the cDNA from major ampullate glands and find evidence for alternative splicing of MaSp2D transcripts into a minor spliceoform lacking the entire repetitive domain as well as the partial terminal regions. Our results not only provide new templates for protein-based materials with tailored properties, but suggest gene and transcriptional diversity of major ampullate silk. [ABSTRACT FROM AUTHOR]

Simple Summary: Spiders are common predators found in almost every type of environment, and are used as model organisms in studies ranging from communication and signalling to biochemical studies on their silk. Orb spiders are particularly interesting, as their web provides a cost-effective way to obtain information on their foraging behaviour. However, studies on short-term behaviours including prey capture and escape behaviours are rare and usually take place in artificial settings, such as laboratories. In this study, we tested a simple methodology using tuning forks that can be used consistently and reliably in the field. The two tuning forks are capable of producing attack (440 Hz) and escape (256 Hz) responses from the spiders. We also used a metal wire as a mechanical stimulus for comparison, which as predicted, was less reliable. We demonstrate the usefulness of the methodology by quantitatively investigating how the size of the spider and the size of its web affect predatory and escape response rates in the autumn spider, although no significant effects of either were found. However, our results confirm the ease by which this simple method can be used to conduct behavioural studies of orb spiders in the wild. Spiders and their webs are often used as model organisms to study a wide range of behaviours. However, these behavioural studies are often carried out in the laboratory, and the few field studies usually result in large amounts of video footage and subsequent labour-intensive data analysis. Thus, we aimed to devise a cost- and time-effective method for studying the behaviour of spiders in the field, using the now almost forgotten method of stimulating webs with tuning forks. Our study looked at the viability of using 256 Hz and 440 Hz tuning forks to stimulate, anti-predatory and predatory responses in the orb web spider Metellina segmentata, respectively. To assess the consistency of the behaviours produced, we compared these to direct mechanical stimulation with a metal wire. The results suggest that the tuning forks produce relatively consistent behaviours within and between two years in contrast to the metal wire. We furthermore found no significant effects of spider length or web area on spider reaction times. However, we found significant differences in reaction times between escape and prey capture behaviours, and between tuning forks and the wire. Thus, we demonstrated the potential of tuning forks to rapidly generate quantitative data in a field setting. [ABSTRACT FROM AUTHOR]

Simple Summary: Spiders often use their webs as sensory mechanisms, obtaining from them such information as the location of prey, the presence of rival spiders, and the characteristics of potential mates. Examining how this information is transmitted through the web and received by spiders is a promising biological area of research that could provide insight into a spider's world and lead to new technologies that leverage these discoveries. In this paper, we develop a novel noncontact technique using two video cameras that is capable of analyzing vibrational signals transmitted through spiderwebs and validate this technique against the current standard of laser Doppler vibrometry. By combining the principles of stereo vision and video vibrometry, we can automatically extract three-dimensional vibrational information at any point in the spiderweb across time, and study how these signals propagate through the web. We show that this technique produces results comparable to those of standard laser vibrometry. From courtship rituals, to prey identification, to displays of rivalry, a spider's web vibrates with a symphony of information. Examining the modality of information being transmitted and how spiders interact with this information could lead to new understanding how spiders perceive the world around them through their webs, and new biological and engineering techniques that leverage this understanding. Spiders interact with their webs through a variety of body motions, including abdominal tremors, bounces, and limb jerks along threads of the web. These signals often create a large enough visual signature that the web vibrations can be analyzed using video vibrometry on high-speed video of the communication exchange. Using video vibrometry to examine these signals has numerous benefits over the conventional method of laser vibrometry, such as the ability to analyze three-dimensional vibrations and the ability to take measurements from anywhere in the web, including directly from the body of the spider itself. In this study, we developed a method of three-dimensional vibration analysis that combines video vibrometry with stereo vision, and verified this method against laser vibrometry on a black widow spiderweb that was experiencing rivalry signals from two female spiders. [ABSTRACT FROM AUTHOR]

In the spider Paratrechalea ornata, males have two gift-giving mating tactics, offering either a nutritive (prey) or a worthless (prey leftovers) silk wrapped gift to females. Both gift types confer similar mating success and duration and afford males a higher success rate than when they offer no gift. If this lack of difference in the reproductive benefits is true, we would expect all males to offer a gift but some males to offer a worthless gift even if prey are available. To test this, we allowed 18 males to court multiple females over five consecutive trials. In each trial, a male was able to produce a nutritive gift (a live housefly) or a worthless gift (mealworm exuviae). We found that, in line with our predictions, 20% of the males produced worthless gifts even when they had the opportunity to produce a nutritive one. However, rather than worthless gifts being a cheap tactic, they were related to a higher investment in silk wrapping. This latter result was replicated for worthless gifts produced in both the presence and absence of a live prey item. We propose that variation in gift-giving tactics likely evolved initially as a conditional strategy related to prey availability and male condition in P. ornata. Selection may then have favoured silk wrapping as a trait involved in female attraction, leading worthless gift-giving to invade. [ABSTRACT FROM AUTHOR]

1. Major floods of riparian and grassland habitats may lead to a shift in the availability of resources (e.g., food, space) that produces cascading effects on the organisms that rely on it. After flooding occurs, particularly in natural grasslands or agricultural fields, massive aggregative spider webs are occasionally observed. However, given it is an infrequent and unpredictable event, it is seldom reported in detail. 2. We characterise two instances of massive web aggregations that followed major floods in grasslands and agricultural fields in Argentina and Uruguay in 2015. In the Argentinean event, we compare the composition of spider assemblages on the webs, in grasses below the webs, and in grasses from nearby habitats, with samples taken in the same location but when the fields were not flooded. 3. The assemblage of spiders in the massive web aggregations largely consisted of immature Diapontia uruguayensis (Lycosidae). In the grass below the webs, we recorded an impressive density of 1007 specimens m−1 belonging to several spider species, 6–15 times the density of similar samples without aggregated webs, co‐occurring and showing low levels of aggression among them. 4. Our observations and review of the literature support the idea massive webs produced by lycosids are a byproduct of an unusually high density of spiders simultaneously attempting to disperse through the air via ballooning and escaping from floods. [ABSTRACT FROM AUTHOR]

Spider web anchors are attachment structures composed of the bi-phasic glue-fiber secretion from the piriform silk glands. The mechanical performance of the anchors strongly correlates with the structural assembly of the silk lines, which makes spider silk anchors an ideal system to study the biomechanical function of extended phenotypes and its evolution. It was proposed that silk anchor function guided the evolution of spider web architectures, but its fine-structural variation and whether its evolution was rather determined by changes of the shape of the spinneret tip or in the innate spinning choreography remained unresolved. Here, we comparatively studied the micro-structure of silk anchors across the spider tree of life, and set it in relation to spinneret morphology, spinning behavior and the ecology of the spider. We identified a number of apomorphies in the structure of silk anchors that may positively affect anchor function: (1) bundled dragline, (2) dragline envelope, and (3) dragline suspension ("bridge"). All these characters were apomorphic and evolved repeatedly in multiple lineages, supporting the notion that they are adaptive. The occurrence of these structural features can be explained with changes in the shape and mobility of the spinneret tip, the spinning behavior, or both. Spinneret shapes generally varied less than their fine-tuned movements, indicating that changes in construction behavior play a more important role in the evolution of silk anchor assembly. However, the morphology of the spinning apparatus is also a major constraint to the evolution of the spinning choreography. These results highlight the changes in behavior as the proximate and in morphology as the ultimate causes of extended phenotype evolution. Further, this research provides a roadmap for future bioprospecting research to design high-performance instant line anchors. [ABSTRACT FROM AUTHOR]

Widow spiders belong to the cosmopolitan genus Latrodectus (Araneae: Theridiidae), of which five species are found in North America. In part due to their medical importance and common occurrence, they are ever-more popular study organisms in a wide variety of fields. However, the literature is widely dispersed, and a broad synthesis has not been attempted since 1970. Here, we review and synthesize published information on the five North American Latrodectus species: L. hesperus, L. mactans, L. variolus, L. bishopi, and the introduced L. geometricus. We focus on distribution, ecology, anatomy, physiology, reproduction, ontogeny, behaviour, web structure, silk, venom, genetics, and phylogeny. We also include some of our own observations on L. hesperus. We conclude by highlighting areas where further research would be especially fruitful. [ABSTRACT FROM AUTHOR]

Animals often compete for resources and territory. Differences in size and body condition often play a crucial role in determining the outcome of these competitions. Web spiders not only create very costly semipermanent territories in the forms of their webs but have been shown able to gather myriad information from chemical cues present on silk. Furthermore, some web spiders are known to invade the webs of conspecifics in lieu of creating their own. We examined whether two pholcid spiders, Pholcus manueli and Pholcus phalangioides , use chemical information about the size and body condition of the web owner to inform their decisions when invading a foreign web. Specifically, we examined whether spiders could gather information about the size and hunger level of a conspecific and whether this information influenced their web-invading behaviour. We also examined whether washing webs with ethanol could remove these effects. We introduced spiders to webs built by conspecifics and recorded their latency to invade the webs. Pholcus manueli invaded webs built by larger conspecifics more slowly while P. phalangioides did not alter invasion latency to larger spiders' webs. Washing webs with ethanol removed this effect. Neither species' behaviour was affected by the hunger level of the web builder. Our results show that P. manueli can determine the size of a conspecific from chemical cues attached to silk and adjust their web invasion behaviour accordingly, but that P. phalangioides does not adjust its behaviour in response to such cues. Importantly, our web-washing results support that chemical cues and not web structure influenced invasion behaviour of P. manueli , giving us a powerful tool for future research. The species level differences suggest separate behavioural strategies between the two similar species and that these strategies may influence the outcome of competitions between the two. • We tested whether pholcids use chemical cues to assess web builder size/condition. • Pholcids assessed the size of conspecifics from chemical cues on empty webs. • The smaller species, P. manueli , invaded webs of smaller conspecifics faster. • Pholcus phalangioides did not adjust behaviour based on web builder size. • Washing webs with ethanol removed chemical cues. [ABSTRACT FROM AUTHOR]

Spiders, assigned to macroconcentrators of heavy metals, are particularly threatened by the toxic effects of these chemicals. Until now, it has not been specified to what extent metals alter the processes proceeding in silk glands and if such changes could consequently influence the chemical and structural properties of the spun web threads. In the present study selected biological properties of Steatoda grossa (Theridiidae) silk yarn after nutritional exposure to copper at sublethal doses (0.234 mM CuSO4) were assessed. It was determined both changes in ultrastructure of ampullate glands and hunting web's architecture as well the cytotoxic effect in model cells (fibroblasts: line ATCC® CCL–1 NCTC clone 929), that were in contact with the analyzed biomaterial. The exposure of spiders to copper caused the occurrence of apoptotic cells in the ampullate glands as well as a significant reduction in the diameter of single fibers in double and multiple connection complexes as compared with control. At both 24 and 72 h of incubation, intensification of apoptotic and necrotic processes was observed in the fibroblast cultures that were remaining in indirect contact with the webs produced by copper–contaminated individuals. In the case of fibroblasts in direct contact with silk from the copper group, a clear cytotoxic effect resulting in an increased frequency of necrosis was observed after 72 h of incubation. The results indicated that copper may change the biological properties of spider silk and compromise its biomaterial properties. [Display omitted] ● The biological quality of spider silk is strongly influenced by copper, even in sublethal doses. ● Copper indirectly alters the architecture of spiders' hunting webs, damaging the silk glands. ● Short-term oral administration of copper weakens the properties of silk as a potential scaffold for cell cultures. ● Identifying the effects of metals on the biological properties of spider silk is important for its potential applications in tissue engineering. [ABSTRACT FROM AUTHOR]

Traps are rarely used by animals, despite the plausible benefits of broadening the number and diversity of prey that sit-and-wait foragers might be able to capture. The most well-known trap building sit-and-wait foragers are among the invertebrates, i.e. antlions, wormlions, glow worms, caddisflies, and spiders. A plausible hypothesis for the paucity of trap building by other animals is that biomechanical limitations render them inefficient or ineffective at catching sufficient prey. Here I examined the literature to make a valued judgement about the validity of this hypothesis. It appears that antlion and wormlion pit traps cannot catch and retain the largest prey they might expect to encounter. Arachnacampa glowworm traps are functionally efficient, facilitated by the animal's bioluminescence. Nevertheless they only function in very moist or humid conditions. Caddisfly traps rely on flowing water to be able to capture their prey. Spiders are exceptional in developing a wide range of prey trapping strategies, from webs with dry adhesives, to sticky orb webs, to modified orb webs, e.g. elongated "ladder" webs, to webs with additional structures, and web aggregations. Some spiders have even redesigned their webs to minimize the high prey escape rates associated with web two dimensionality. These webs nevertheless are constructed and used at specific costs. While hard data across all of the invertebrate predators is lacking, there seems to be credence in the hypothesis that the biomechanical limitations placed on trap functionality can explain their limited use among animals. [ABSTRACT FROM AUTHOR]

Silk decorations in webs of orb-weaving spiders are considered visual signals. However, high pattern variation reduces the plausibility of a single signal function, and accordingly, current literature often presents contradicting explanations. The controversial question is whether specific web decoration shapes also serve specific functions or whether various arrangements can serve a single function. I studied inherent characteristics of the variation of silk decoration shapes in Argiope bruennichi (Scopoli, 1772), in the field and under invariant laboratory conditions. The results show, that even within a few days and with a small repertoire of patterns, A. bruennichi frequently varies the decoration shape. Field and laboratory data both reveal that this variation follows a predictable pattern, significantly differing from random. Spiders show a preference for two-banded decorations, omitting decorating altogether rather than building one-banded decorations. Since the shape matters to the spiders, this supports the idea of a single signal function in spite of the presence of web decoration pattern variability. [ABSTRACT FROM AUTHOR]

Most spiders spin multiple types of silk, including silks for reproduction, prey capture, and draglines. Spiders are a megadiverse group and the majority of spider silks remain uncharacterized. For example, nothing is known about the silk molecules of Tengella perfuga, a spider that spins sheet webs lined with cribellar silk. Cribellar silk is a type of adhesive capture thread composed of numerous fibrils that originate from a specialized plate-like spinning organ called the cribellum. The predominant components of spider silks are spidroins, members of a protein family synthesized in silk glands. Here, we use silk gland RNA-Seq and cDNA libraries to infer T. perfuga silks at the protein level. We show that T. perfuga spiders express 13 silk transcripts representing at least five categories of spider silk proteins (spidroins). One category is a candidate for cribellar silk and is thus named cribellar spidroin (CrSp). Studies of ontogenetic changes in web construction and spigot morphology in T. perfuga have documented that after sexual maturation, T. perfuga females continue to make capture webs but males halt web maintenance and cease spinning cribellar silk. Consistent with these observations, our candidate CrSp was expressed only in females. The other four spidroin categories correspond to paralogs of aciniform, ampullate, pyriform, and tubuliform spidroins. These spidroins are associated with egg sac and web construction. Except for the tubuliform spidroin, the spidroins from T. perfuga contain novel combinations of amino acid sequence motifs that have not been observed before in these spidroin types. Characterization of T. perfuga silk genes, particularly CrSp, expand the diversity of the spidroin family and inspire new structure/function hypotheses. [ABSTRACT FROM AUTHOR]

The extraordinary mechanical properties of spider dragline silk are dependent on the highly repetitive sequences of the component proteins, major ampullate spidroin 1 and 2 (MaSp2 and MaSp2). MaSp sequences are dominated by repetitive modules composed of short amino acid motifs; however, the patterns of motif conservation through evolution and their relevance to silk characteristics are not well understood. We performed a systematic analysis of MaSp sequences encompassing infraorder Araneomorphae based on the conservation of explicitly defined motifs, with the aim of elucidating the essential elements of MaSp1 and MaSp2. The results show that the GGY motif is nearly ubiquitous in the two types of MaSp, while MaSp2 is invariably associated with GP and di-glutamine (QQ) motifs. Further analysis revealed an extended MaSp2 consensus sequence in family Araneidae, with implications for the classification of the archetypal spidroins ADF3 and ADF4. Additionally, the analysis of RNA-seq data showed the expression of a set of distinct MaSp-like variants in genus Tetragnatha. Finally, an apparent association was uncovered between web architecture and the abundance of GP, QQ, and GGY motifs in MaSp2, which suggests a co-expansion of these motifs in response to the evolution of spiders' prey capture strategy. [ABSTRACT FROM AUTHOR]

The abundance of sperm relative to eggs selects for males that maximize their number of mates and for females that choose high quality males. However, in many species, males exercise mate choice, even when they invest little in their offspring. Sexual cannibalism may promote male choosiness by limiting the number of females a male can inseminate and by biasing the sex ratio toward females because, while females can reenter the mating pool, cannibalized males cannot. These effects may be insufficient for male choosiness to evolve, however, if males face low sequential encounter rates with females. We hypothesized that sexual cannibalism should facilitate the evolution of male choosiness in group living species because a male is likely to encounter multiple receptive females simultaneously. We tested this hypothesis in a colonial orb-weaving spider, Cyrtophora citricola, with a high rate of sexual cannibalism. We tested whether mated females would mate with multiple males, and thereby shift the operational sex ratio toward females. We also investigated whether either sex chooses mates based on nutritional state and age, and whether males choose females based on reproductive state. We found that females are readily polyandrous and exhibit no mate choice related to male feeding or age. Males courted more often when the male was older and the female was younger, and males copulated more often with well-fed females. The data show that males are choosier than females for the traits we measured, supporting our hypothesis that group living and sexual cannibalism may together promote the evolution of male mate choice. [ABSTRACT FROM AUTHOR]

Spiders can produce up to seven different types of silk, each with different properties-- some silks are sticky and elastic, while others are dry and tough. This paper examines and compares two ways in which humans have used this diverse material to design fabrics: the weaving of dry silk threads, and the layering of complete spider webs. The study investigates how these fabrics are formed by both the properties of the material and differing human perceptions of it, and the actions of the spiders themselves. It proposes that in order to develop a broad ecological approach to design and design history, attention should be given to the role of non-human animals. [ABSTRACT FROM AUTHOR]

Y-maze choice experiment were used to examine the prey-attraction hypothesis for the function of stabilimentum on the orb-webs of Argiope aemula and A. luzona. Fruit flies (Drosophila spp.), common prey species for spiders were used to determine whether webs with stabilimenta attract more flies in Y-maze choice experiment. The result showed that under well-lit condition (bright light), webs with stabilimenta significantly attracted more prey compared to those without stabilimenta in A. aemula and A. luzona. However, regarding the prey capture rate in bright light, only A. aemula showed an increased in the number of prey captured in decorated webs. Under dim condition, the results still showed a significant difference in the number of approaching prey, but not in the number of prey captured by the webs. In both species, the number of prey approached and intercepted in the decorated webs were higher in well-lit condition than in dim condition, suggesting that fruit flies are attracted to webs with stabilimenta in both species studied. Our data is congruent with the prey-attraction hypothesis as function of stabilimentum. [ABSTRACT FROM AUTHOR]

Spider dragline silk is a natural fiber that has excellent tensile properties; however, it is difficult to produce artificially as a long, strong fiber. Here, the spider (Araneus ventricosus) dragline protein gene was cloned and a transgenic silkworm was generated, that expressed the fusion protein of the fibroin heavy chain and spider dragline protein in cocoon silk. The spider silk protein content ranged from 0.37 to 0.61% w/w (1.4–2.4 mol%) native silkworm fibroin. Using a good silk-producing strain, C515, as the transgenic silkworm can make the raw silk from its cocoons for the first time. The tensile characteristics (toughness) of the raw silk improved by 53% after the introduction of spider dragline silk protein; the improvement depended on the quantity of the expressed spider dragline protein. To demonstrate the commercial feasibility for machine reeling, weaving, and sewing, we used the transgenic spider silk to weave a vest and scarf; this was the first application of spider silk fibers from transgenic silkworms. [ABSTRACT FROM AUTHOR]

Animals that build structures have only two ways of obtaining their building materials: collecting them from the environment or secreting them. We identify a clear pattern among invertebrates: collected materials dominate in structures that bear loads predominantly in compression, whereas self-secreted materials dominate in structures that bear loads in tension. Among vertebrates, by contrast, structures in tension are much less common and may make use of either self-secreted or collected materials. Two possible explanations are examined for the difference between invertebrates and vertebrates. It may be that there has been evolutionary constraint on bodily secretions of vertebrates. Alternatively, the cost-effectiveness of self-secreted building materials diminishes with the load they bear in tension, and most vertebrates, because of their characteristically greater weight compared with invertebrates, exceed the viability threshold. Invertebrates have adapted biochemically varied secretions from a variety of glands to perform specialized mechanical roles. However, vertebrates have secretions with the potential to become building materials, in particular keratin, but only mucus-like secretions have evolved as building materials. The cost of suspended structures is predicted to become relatively greater with increased weight, whilst it will also become more difficult to find supports rigid enough to resist the forces they impose. This conforms to the relatively small size and small number of vertebrate structures in tension. The much larger, heavier suspended structures built by some social insects demonstrate that ecological factors may have important effects on the determination of weight thresholds. © 2014 The Linnean Society of London, Biological Journal of the Linnean Society, 2014, 112, 625-639. [ABSTRACT FROM AUTHOR]

Like many biomaterials, spider silk responds to water through softening and swelling. Major ampullate silk, the main structural element of most prey capture webs, also shrinks dramatically if unrestrained or develops high tension if restrained, a phenomenon called 'supercontraction'. While supercontraction has been investigated for over 30?years, its consequences for web performance remain controversial. Here, we measured prey capture performance of dry and wet (supercontracted) orb webs of Argiope and Nephila using small wood blocks as prey. Prey capture performance significantly increased at high humidity for Argiope while the improvement was less dramatic for Nephila. This difference is likely due to Argiope silk supercontracting more than Nephila silk. Web deflection, measured as the extension of the web upon prey impact, also increased at high humidity in Argiope, suggesting that silk softening upon supercontraction explains the improved performance of wet webs. These results strongly argue that supercontraction is not detrimental to web performance. [ABSTRACT FROM AUTHOR]

Spiders in the Orbiculariae spin orb webs that dissipate the mechanical energy of their flying prey, bringing the insects to rest and retaining them long enough for the spider to attack and subdue their meals. Small prey are easily stopped by webs but provide little energetic gain. While larger prey offer substantial nourishment, they are also challenging to capture and can damage the web if they escape. We therefore hypothesized that spider orb webs exhibit properties that improve their probability of stopping larger insects while minimizing damage when the mechanical energy of those prey exceeds the web's capacity. Large insects are typically both heavier and faster flying than smaller prey, but speed plays a disproportionate role in determining total kinetic energy, so we predicted that orb webs may dissipate energy more effectively under faster impacts, independent of kinetic energy per se. We used high-speed video to visualize the impact of wooden pellets fired into orb webs to simulate prey strikes and tested how capture probability varied as a function of pellet size and speed. Capture probability was virtually nil above speeds of ~3 m s-1. However, successful captures do not directly measure the maximum possible energy dissipation by orb webs because these events include lower-energy impacts that may not significantly challenge orb web performance. Therefore, we also compared the total kinetic energy removed from projectiles that escaped orb webs by breaking through the silk, asking whether more energy was removed at faster speeds. Over a range of speeds relevant to insect flight, the amount of energy absorbed by orb webs increases with the speed of prey (i.e. the rates at which webs are stretched). Orb webs therefore respond to faster - and hence higher kinetic energy - prey with better performance, suggesting adaptation to capture larger and faster flying insect prey. This speed-dependent toughness of a complex structure suggests the utility of the intrinsic toughness of spider silk and/or features of the macro-design of webs for high-velocity industrial or military applications, such as ballistic energy absorption. [ABSTRACT FROM AUTHOR]

Transparent, microscopic spider web silk fibers were used to softly intrude into the propagating path ofN-slit interferograms. The resulting interferograms, with superimposed diffractive signals, were recorded using digital means and reproduced usingN-slit interferometric calculations. We also show, for the first time, very slight and subtle alterations of the propagating interferograms via the soft insertion of spider web silk fibers into the intra-interferometric path. The experiments were performed at an overall intra-interferometric propagation path length of 7.235 m. [ABSTRACT FROM AUTHOR]